Skeletal reconstruction cages

ABSTRACT

Skeletal reconstruction cages include a central body having first and second ends, a first end cap coupled to one end of the central body, and a second end cap coupled to the other end of the central body. At least two of the central body, first end cap, and second end cap are formed from bone. Each of the central body, first end cap, and second end cap may be provided in different sizes so that cages with varying overall heights, and related angulations, may be created.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/730,011, which is a divisional of U.S. Pat. No. 6,660,038, which inturn claims the benefit of U.S. Provisional Application No. 60/191,099,filed Mar. 22, 2000, under 35 U.S.C. §119(e). The entire contents ofthese applications are expressly incorporated herein by referencethereto.

FIELD OF THE INVENTION

The invention relates to an implant for orthopedic applications. Moreparticularly, the invention is related to skeletal reconstruction cagesformed from bone for filling vacancies in bone tissue.

BACKGROUND OF THE INVENTION

Bone grafts have become an important and accepted means for treatingbone fractures and defects. In the United States alone, approximatelyhalf a million bone grafting procedures are performed annually, directedto a diverse array of medical interventions for complications such asfractures involving bone loss, injuries or other conditionsnecessitating immobilization by fusion (such as for the spine orjoints), and other bone defects that may be present due to trauma,infection, or disease. Bone grafting involves the surgicaltransplantation of pieces of bone within the body, and generally iseffectuated through the use of graft material acquired from a humansource. This is primarily due to the limited applicability ofxenografts, transplants from another species.

Orthopedic autografts or autogenous grafts involve source bone acquiredfrom the same individual that will receive the transplantation. Thus,this type of transplant moves bony material from one location in a bodyto another location in the same body, and has the advantage of producingminimal immunological complications. It is not always possible or evendesirable to use an autograft. The acquisition of bone material from thebody of a patient typically requires a separate operation from theimplantation procedure. Furthermore, the removal of material, oftentimesinvolving the use of healthy material from the pelvic area or ribs, hasthe tendency to result in additional patient discomfort duringrehabilitation, particularly at the location of the material removal.Grafts formed from synthetic material have also been developed, but thedifficulty in mimicking the properties of bone limits the efficacy ofthese implants.

As a result of the challenges posed by autografts and synthetic grafts,many orthopedic procedures alternatively involve the use of allografts,which are bone grafts from other human sources (normally cadavers). Thebone grafts, for example, are placed in a host bone and serve as thesubstructure for supporting new bone tissue growth from the host bone.The grafts are sculpted to assume a shape that is appropriate forinsertion at the fracture or defect area, and often require fixation tothat area as by screws or pins. Due to the availability of allograftsource material, and the widespread acceptance of this material in themedical community, the use of allograft tissues is certain to expand inthe field of musculoskeletal surgery.

Various spinal conditions are managed, in part, by the introduction ofbone grafts. For example, degeneration in the intervertebral discs ofthe cervical spine and the joints between the vertebrae can result inabnormal pressure on the spinal cord that must be relieved with surgicalintervention. It is known to ease undesirable pressure by surgicallyremoving the degenerated tissue, such as the vertebrae, and replacingthe surgically-created void with a bone graft. Other reasons forsurgical removal of spinal tissue include disease such as cancer orother trauma. The procedure of removing vertebral bodies and the discsbetween each vertebra is known as a corpectomy, i.e., a removal of thebody. A bone autograft suitable for this purpose is often taken from apatient's pelvis or leg bones. Typically, the graft is in the form of astrut or block of bone, which is shaped to fit into adjoining vertebralbodies to fill the empty space and maintain proper spacing betweenremaining vertebrae. The strut also preserves proper anatomicorientation, while promoting bony fusion with surroundings forsubsequent stability.

Fusion procedures may be performed in the cervical, thoracic or lumbarspine, and following placement of the bone graft, a unicortical lockingplate is typically installed over the graft by screwing it into theadjoining vertebral bodies. The plate may enhance stability until bonyfusion occurs, as well as prevent dislodgment of the graft.

The frequency of corpectomies has created a demand for improved implantdesigns as well as novel approaches to forming the implants, such aswith allografts. In order to provide such implants, an understanding ofthe sources of allograft bone and the characteristics of bone is useful.

Different bones of the body such as the femur (thigh), tibia and fibula(leg), humerus (upper arm), radius and ulna (lower arm) have geometriesthat vary considerably. In addition, the lengths of these bones vary;for example, in an adult the lengths may vary from 47 centimeters(femur) to 26 centimeters (radius). Furthermore, the shape of the crosssection of each type of bone varies considerably, as does the shape ofany given bone over its length. While a femur has a generally roundedouter shape, a tibia has a generally triangular outer shape. Also, thewall thickness varies in different areas of the cross-section of eachbone. Thus, the use of any given bone to produce an implant componentmay be a function of the bone's dimensions and geometry. Machining ofbones, however, may permit the production of implant components withstandardized dimensions.

As a collagen-rich and mineralized tissue, bone is composed of aboutforty percent organic material (mainly collagen), with the remainderbeing inorganic material (mainly a near-hydroxyapatite compositionresembling 3Ca₃(PO₄)₂Ca(OH)₂). Structurally, the collagen assumes afibril formation, with hydroxyapatite crystals disposed along the lengthof the fibril, and the individual fibrils are disposed parallel to eachother forming fibers. Depending on the type of bone, the fibrils areeither interwoven, or arranged in lamellae that are disposedperpendicular to each other.

There is little doubt that bone tissues have a complex design, and thereare substantial variations in the properties of bone tissues withrespect to the type of bone (i.e., leg, arm, vertebra) as well as theoverall structure of each type. For example, when tested in thelongitudinal direction, leg and arm bones have a modulus of elasticityof about 17 to 19 GPa, while vertebra tissue has a modulus of elasticityof less than 1 GPa. The tensile strength of leg and arm bones variesbetween about 120 MPa and about 150 MPa, while vertebra have a tensilestrength of less than 4 MPa. Notably, the compressive strength of bonevaries, with the femur and humerus each having a maximum compressivestrength of about 167 MPa and 132 MPa respectively. Again, the vertebrahave a far lower compressive strength of no more than about 10 MPa.

With respect to the overall structure of a given bone, the mechanicalproperties vary throughout the bone. For example, a long bone (leg bone)such as the femur has both compact bone and spongy bone. Cortical bone,the compact and dense bone that surrounds the marrow cavity, isgenerally solid and thus carries the majority of the load in majorbones. Cancellous bone, the spongy inner bone, is generally porous andductile, and when compared to cortical bone is only about one-third toone-quarter as dense, one-tenth to one-twentieth as stiff, but fivetimes as ductile. While cancellous bone has a tensile strength of about10-20 MPa and a density of about 0.7, cortical bone has a tensilestrength of about 100-200 MPa and a density of about 2. Additionally,the strain to failure of cancellous bone is about 5-7%, while corticalbone can only withstand 1-3% strain before failure. It should also benoted that these mechanical characteristics may degrade as a result ofnumerous factors such as any chemical treatment applied to the bonematerial, and the manner of storage after removal but prior toimplantation (i.e. drying of the bone).

Notably, implants of cancellous bone incorporate more readily with thesurrounding host bone, due to the superior osteoconductive nature ofcancellous bone as compared to cortical bone. Furthermore, cancellousbone from different regions of the body is known to have a range ofporosities. Thus, the design of an implant using cancellous bone may betailored to specifically incorporate material of a desired porosity.

It is essential to recognize the distinctions in the types andproperties of bones when considering the design of implants. Surgeonsoften work with bones using similar tools as would be found incarpentry, adapted for use in the operating room environment. Thissuggests that bones have some properties which are similar to some typesof wood, for example ease in sawing and drilling. Notably, however, aremany differences from wood such as the abrasive nature of hydroxyapatiteand the poor response to local heating during machining of a bone. Thecombination of tensile and compressive strengths found in bone,resulting from the properties of the collagen and hydroxyapatite, isthus more aptly compared to the high tensile and compressive strengthsfound in reinforced concrete, due to steel and cement. Furthermore,while wood is readily available in considerable quantity, bone materialis an extremely limited resource that must be used in an extremelyefficient manner.

Various types of bone grafts are known. For example, as disclosed inU.S. Pat. No. 5,989,289 to Coates et al., a spinal spacer includes abody formed of a bone composition such as cortical bone. The spacer haswalls that define a chamber that is sized to receive an osteogeniccomposition to facilitate bone growth.

U.S. Pat. No. 5,899,939 to Boyce et al. discloses a bone-derived implantfor load-supporting applications. The implant has one or more layers offully mineralized or partially demineralized cortical bone and,optionally, one or more layers of some other material. The layersconstituting the implant are assembled into a unitary structure, as byjoining layers to each other in edge-to-edge fashion in a manneranalogous to planking.

With a rapidly increasing demand in the medical profession for devicesincorporating bone material, the tremendous need for the tissue materialitself, particularly allograft tissue material, presents a considerablechallenge to the industry that supplies the material. Due to the sizeand shape of the bones from which the material is harvested, and thedimensional limitations of any particular type of bone in terms ofnaturally occurring length and thickness (i.e. cortical or cancellous),there is a need for a means by which individual bone fragments can becombined to form larger, integral implants that are more suitable foruse in areas of larger fractures or defects. For example, the size ofcortical bone fragments needed to repair a fracture or defect site isoften not available in a thick enough form. While multiple fragments maytogether meet the size and shape requirements, several prominentconcerns have placed a practical limitation on the implementation ofthis concept. There is considerable uncertainty regarding the structuralintegrity provided by fragments positioned adjacent to one anotherwithout bonding or other means of securing the fragments to each other.Moreover, there is concern over the possibility that a fragment may slipout of position, resulting in migration of the fragment and possiblefurther damage in or near the area of implantation.

In addition, due to the geometry of bones such as the femur and tibia,all portions of the bones are not readily usable as a result of sizelimitations. Thus, prior art implants, specifically allografts, areproduced with an inefficient use of source bones.

There is a need for new approaches to working with and processingtissues, in particular allograft material, especially with regard tomachining, mating, and assembling bone fragments. Specifically, there isa need for an implant that allows more efficient use of source material.More specifically, there is a need for an implant that is an integratedimplant comprising two or more bone fragments that are interlocked toform a mechanically effective, strong unit.

Furthermore, there is a need for implants that may span the vacancybetween two bony regions, such as for use in corpectomies, long bonereconstruction, tibial osteotomies, filling bony defects, and interbodyfusions. There is also a need for skeletal reconstruction implantsformed of bone and other materials that permit a wide range of angles,heights, and configurations to be accommodated so that a particularanatomical defect may be spanned.

SUMMARY OF THE INVENTION

The present invention is related to a corpectomy cage including acentral body having first and second ends, a first end cap, and a secondend cap. The first end cap is coupled to one end of the central body andthe second end cap is coupled to the other end of the central body. Thefirst end may be disposed in a first body plane and the second end maybe disposed in a second body plane, the first and second planesconverging with respect to each other. A first alignment plane extendingperpendicular to the central axis is disposed at a first angle withrespect to the first body plane, and a second alignment plane extendingperpendicular to the central axis is disposed at a second angle withrespect to the second body plane, with the first and second angles beingabout the same. The first and second angles may be between about 1° andabout 3°. The end caps each include a top face disposed in a first capplane and a bottom face disposed in a second cap plane, the first andsecond cap planes being disposed at a cap angle with respect to eachother. The first angle, second angle, and cap angle may be about thesame and between about 1° and about 3°. In some embodiments, one of thecentral body and an end cap has a protrusion and the other further has arecess, with the protrusion being configured and dimensioned for matingwith the recess. The protrusion and recess may be non-circular, and ifthe protrusion is symmetrical about a central protrusion axis, theprotrusion is selectably positionable within the recess in twoorientations.

The central shaft may be threadably associated with at least one endcap, and each end cap may include a migration-resistant surface. Also,the central body may have a hole extending from the first end to thesecond end, with the hole disposed about a central axis. The skeletalreconstruction cage may further include a core configured anddimensioned to be received in the hole, with the core being formed ofbone.

In some embodiments, the skeletal reconstruction cage includes a core,the central body includes a hole extending from the first end toward thesecond end with the hole disposed about a central axis, and at least oneof the central body, first end cap, second end cap, and core is formedfrom bone. The core is configured and dimensioned to be received in thehole. At least one of the central body, first end cap, second end cap,and core may be formed of cancellous bone or cortical bone of autograft,allograft, or xenograft bone tissue and may be partially demineralizedor demineralized bone tissue. At least two of the central body, firstend cap, second end cap, and core may be fastened together with at leastone fastener selected from a screw, key, pin, peg, rivet, cotter, nail,spike, bolt, stud, staple, boss, clamp, clip, dowel, stake, hook,anchor, tie, band, crimp, and wedge. At least two of the central body,first end cap, second end cap, and core may be bonded together with abonding agent, and at least one may be at least partially dehydrated tofit against a surrounding mating surface or to mate with anothercomponent.

The present invention is also related to a method of providing variablefit for a skeletal reconstruction cage. The method includes: providing afirst set of central bodies, each central body having a differentmaximum height from one another; providing a second set of top end capsof variable sizes, each top end cap having a different maximum heightfrom one another; providing a third set of bottom end caps of variablesizes, each bottom end cap having a different maximum height from oneanother; selecting the central body, top end cap, and bottom end capthat provide preferred skeletal reconstruction cage height when coupledtogether; coupling the first and second end caps to the central body toform a first skeletal reconstruction cage, with the end caps disposed onopposing ends of the central body. The method may further include:providing a fourth set of inserts of variable sizes, each insert havinga different maximum height from one another; selecting the insert thatprovides preferred height when disposed in a hole in the central body;and inserting the insert in the central body. At least one of thecentral body, top end cap, bottom end cap, and insert may be formed ofbone.

In addition, the present invention is related to a skeletalreconstruction cage including a central body having first and secondfree ends, with each end including a receiving region. The cage alsoincludes a first end cap coupled to one free end of the central body andhaving a first protruding region, and a second end cap coupled to theother free end of the central body and having a second protrudingregion. The first protruding region and the second protruding region areconfigured and dimensioned to be received in the receiving regions, andeach of the regions is symmetrical about at least one central planeextending generally perpendicular to the first and second free ends. Insome embodiments, at least one of the central body, first end cap, andsecond end cap is formed from bone.

Furthermore, the present invention is related to an end cap for use witha skeletal reconstruction cage. The end cap includes a cap body having atop face disposed in a first cap plane and a bottom face disposed in asecond cap plane transverse to the first cap plane, with the first andsecond cap planes being disposed at a cap angle with respect to eachother. The cap angle may be between about 1° and about 3°, and the capbody may be formed of bone.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

FIG. 1A shows a side view of a central shaft for use with a skeletalreconstruction cage of the present invention;

FIG. 1B shows a top view of the central shaft of FIG. 1A;

FIG. 2A shows a side view of an end cap of the present invention for usewith the central shaft of FIG. 1A;

FIG. 2B shows a top view of the end cap of FIG. 2A;

FIGS. 3A to 3C show side views of central shafts with a pair of end capsdisposed thereon;

FIG. 3D shows a side view of a skeletal reconstruction cage disposedbetween a pair of vertebral bodies;

FIG. 4A shows a washer-like structure for use with a skeletalreconstruction cage of the present invention;

FIG. 4B shows a side view of a skeletal reconstruction cage thatincludes a pair of washer-like structures;

FIG. 5A shows a side view of another central shaft for use with acorpectomy cage of the present invention;

FIG. 5B shows a top view of the central shaft of FIG. 5A;

FIG. 6A shows a top view of an end cap of the present invention for usewith the central shaft of FIG. 5A;

FIG. 6B shows a side, cross-sectional view of the end cap of FIG. 6Ataken through line VIB-VIB;

FIG. 6C shows a side, cross-sectional view of the end cap of FIG. 6Ataken through line VIC-VIC;

FIG. 6D shows a side, cross-sectional view of the end cap of FIG. 6Ataken through line VID-VID;

FIG. 6E shows a side view of the end cap of FIG. 6A;

FIG. 6F shows a side view of a central shaft with a pair of end capsdisposed thereon;

FIG. 6G shows a side view of a curved central shaft with a pair of endcaps disposed thereon;

FIG. 7A shows a top view of another end cap of the present invention;

FIG. 7B shows a side view of the end cap of FIG. 7A;

FIG. 7C shows a side, cross-sectional view of the end cap of FIG. 7Ataken through line VIIC-VIIC;

FIG. 7D shows another side view of the end cap of FIG. 7A;

FIG. 7E shows a side, cross-sectional view of the end cap of FIG. 7Ataken through line VIIE-VIIE;

FIGS. 8A and 8B show additional embodiments of skeletal reconstructioncages of the present invention;

FIG. 8C shows a generally C-shaped support member for use with theskeletal reconstruction cages of FIGS. 8A and 8B;

FIG. 9 shows a partial exploded side view of a long bone with anadditional skeletal reconstruction cage of the present inventiondisposed therein;

FIGS. 10A to 10D show inserts formed according to the present inventionfor use with skeletal reconstruction cages;

FIG. 10E shows a skeletal reconstruction cage with an insert retainedtherein according to the present invention; and

FIGS. 10F to 10H show additional inserts formed according to the presentinvention for use with skeletal reconstruction cages.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Any of a wide variety of different implant structures, particularlyallograft, autograft, and/or xenograft implant structures, can beprepared according to the teachings of the present invention. While arepresentative selection of implant structures are described anddepicted herein, additional disclosure is found in U.S. ProvisionalApplication No. 60/191,099 filed Mar. 22, 2000, which is herebyincorporated herein in its entirety by reference, including all figures.

As used in the description of the present invention, the words fitting,interfitting, mating, locking, interlocking, meshing, and interlacingare all used generically to describe the joining of bone sections orpieces together. Thus, these words are not limited to the use of anyparticular manner of joining. Thus, for example, the press-fitting ofone bone section within a cavity formed in another bone section may bedescribed using any of the above-mentioned terms. In addition, althoughvarious preferred mechanical fastening approaches are described, thepresent invention allows the use of any mechanical device for joiningtwo or more separate parts of an article or structure. Such mechanicaldevices include, but are not limited to the following: screws, keys,pins, pegs, rivets, cotters, nails, spikes, bolts, studs, staples,bosses, clamps, clips, dowels, stakes, hooks, anchors, ties, bands, andcrimps. Also, bonding agents or other chemical means for joining twoseparate parts may be employed alone or in combination with themechanical devices. Thus, as appropriate, the means disclosed herein forfixing bone sections to each other may be substituted, as with theabove-mentioned mechanical devices, bonding devices, or chemical means.Furthermore, although particular types of joints are disclosed, thepresent invention is directed to the creation of implants that may bejoined using other joints.

While the present invention is preferably directed to the creation ofimplants from allograft material, the present invention may also beapplied to implants that utilize other materials, including but notlimited to the following: xenograft, autograft, metals, alloys,ceramics, polymers, composites, and encapsulated fluids or gels.Furthermore, the implants described herein may be formed of materialswith varying levels of porosity, such as by combined bone sections fromdifferent bones or different types of tissue having varying levels ofporosity. For example, cancellous bone is available in a range ofporosities based on the location in the body from which the bone isharvested. Extremely porous cancellous bone may be harvested fromvarious areas such as the iliac crest, while less porous bone may beharvested from areas such as a tibial condyle. Thus, the materialsproperties—particularly the porosity—of the bone components may beselected to meet the needs of a given application.

Cancellous bone components may be attached to syringes or aspirators,and blood or other fluids such as bone-growth inducing substances may bedrawn into the components. The use of mechanically applied pressure,such as with aspiration devices, permits a greater degree of fluidabsorption and/or concentration to be achieved than otherwise readilyobtainable by soaking bone in such fluids without applying pressure froma device. In embodiments of the present invention that include hollowregions, a component of cancellous bone formed using the aforementionedtechnique may be inserted therein.

Also, the implants described herein may be formed of bone materials withvarying mineral content. For example, cancellous or cortical bone may beprovided in natural, partially demineralized, or demineralized states.Demineralization is typically achieved with a variety of chemicalprocessing techniques, including the use of an acid such as hydrochloricacid, chelating agents, electrolysis or other treatments. Thedemineralization treatment removes the minerals contained in the naturalbone, leaving collagen fibers with bone growth factors including bonemorphogenic protein (BMP). Variation in the mechanical properties ofbone sections is obtainable through demineralization. Advantageously,use of a demineralizing agent on natural bone transforms the propertiesof the bone from a stiff structure to a relatively pliable structurewhen it is hydrated. Some portions of interfitting bone components maybe demineralized in order to achieve improved interfitting. For example,a tissue form may include two bone components having portions that arecoupled together with an interference fit. The interference fit may beenhanced if the surface region of one of the components is demineralizedso that it is pliable and exhibits some elasticity and/or malleability.

In addition, while many of the embodiments described herein show bonecomponents disposed at right angles, or joints formed with right angles,angles that are greater or less than ninety degrees may alternatively beused in implants of the present development. For example, implants aregenerally described herein for use in the spine with total angulationsof less than about 10°. However, the cages of the present invention mayalso mate with defect faces at significantly greater angles. Long bonedefects, breaks, or other vacancies formed by bone tissue removal, forexample, may require cages that mate at angles between about 0° andabout 90°. Tibial osteotomies and femoral voids may require larger cagesthan discussed herein, as well as different angulation. Similarly, otherbony defects or interbody fusions may use cages of the general structuredisclosed herein, but having different dimensional requirements. Otherapplications may include the use of cages in regions in which vertebralbodies have been partially removed.

The components that are used to create implants of the present inventionmay all be formed from cortical bone, all from cancellous bone, or acombination of components formed from cortical and cancellous bone. Theinterfitting of the components may be achieved through a variety ofmeans, including but not limited to the following: pinning, bonding witha suitable bone bonding agent or chemical means, press fitting,threadably engaging (as by helically screwing one component intoanother), snap fitting, inserting a tapered component into a componentwith a matching inner surface, or other interlocking means such as willbe described in other embodiments. Serrations, ribbing, scoring, orother undulating features may be used on edges or faces of bonecomponents to provide positive interlocking or friction fits betweencomponents. While the present development preferably allows the creationof implants from all bone material, it is also anticipated that one ormore components used to create the implants may be formed of non-bonematerial such as a synthetic or other material. Thus, while the implantsdisclosed herein are typically described as being formed primarily frombone, the implants alternatively may be formed in whole or in part fromother materials such as hydroxyapatite, metal, resorbable material,polymer, and ceramic, and may additionally incorporate bone chips, boneparticulate, bone fibers, bone growth materials, and bone cement. Also,while solid-walled structures are described herein, the structuresoptionally may include perforations extending from outer to innersurfaces, or recesses formed in outer surfaces that do not extendthrough inner surfaces. Geometries such as circular depressions, dimplesformed from a spherical geometry, diamond shapes, or rectangular shapesmay be used.

Bones suitable for forming implants of the present invention include aradius, humerus, tibia, femur, fibula, or ulna, although other bones maybe used.

The moisture content of the bone sections also may be varied toadvantageously permit improved interlocking. Bone sections initially maybe provided with moisture content as follows: (1) bone in the naturalstate fresh out of the donor without freezing, (2) bone in the frozenstate, typically at −40° C., with moisture content intact, (3) bone withmoisture removed such as freeze-dried bone, and (4) bone in the hydratedstate, such as when submersed in water. The expansion and contractionproperties that can be obtained from bone during heating, cooling,dehydrating, and hydrating permit an alternate approach to achieving atight press-fit. In addition, the use of such approaches can provide atighter press-fit than otherwise obtainable, as well as decrease themanufacturing tolerances required for mating sections of bone.

Turning now to FIGS. 1 to 8, cages for use in spinal fusions aredescribed. While cages for use in the thoracic and lumbar regions of thespine are shown and described, the cages of the present invention alsomay be used in the cervical region of the spine, as well as in otherregions of the body such as the long bones, as discussed previously.Although the spinal cages disclosed herein are particularly suited touse in the spine for addressing corpectomies, the cages are referred toherein as skeletal reconstruction cages due to the potential use for thecages in other regions of the body.

Referring to FIGS. 1-3, a skeletal reconstruction cage suitable for usein the thoracic region of the spine is shown. In a preferred embodiment,the skeletal reconstruction cage is formed from cortical bone. Turningto FIGS. 1A and 1B, a central shaft 10 includes a top face 12 and abottom face 14, which preferably are nonparallel. In an alternateembodiment, faces 12, 14 may be generally parallel; angulation may beachieved by choosing suitable geometry for end caps that abut faces 12,14. Top face 12 is disposed in a top plane 13 that is preferably slopedat an angle θ₁ with respect to a horizontal plane 16 extending from thehighest vertical point 18 of central shaft 10. Similarly, bottom face 14is disposed in a plane 15 that is preferably sloped in convergingorientation with respect to top face 12 at the same angle θ₁ withrespect to a horizontal plane 20 extending from the lowest verticalpoint 22 of central shaft 10. In alternate embodiments, top and bottomfaces 12, 14, respectively, may be sloped at different angles.Preferably, angle θ₁ is between about 1° and about 2°, and morepreferably about 1.5°. However, vacancies resulting from removal of bonetissue due to cancer or vacancies resulting from deformities may requirethat significantly greater angulation be provided. With such anorientation of top and bottom faces 12, 14, respectively, central shaft10 has a minimum longitudinal height L₁ and a maximum longitudinalheight L₁+2δ, the change in height from L₁ resulting from an increase inheight of δ for each angle θ₁.

Central shaft 10 is disposed about a central axis 24 and preferably hasan outer surface 26 that is generally cylindrical. Alternatively, outersurface 26 may conform to the natural shape of a bone, or it may be akidney shape, trapezoidal shape, or other geometry. A hole 28 extendsfrom top face 12 to bottom face 14. Hole 28 includes a first portion 30with a wall 32 that is generally parallel to outer surface 26 anddefines a first inner diameter D₁ that is preferably between about 11 mmand 13 mm. Central shaft 10 may be formed, for example, from a humerus.Alternate embodiments with a central shaft 10 may be formed from thecross section of a bone; if the natural anatomical geometry of the bonecanal and/or outer surface of the bone is preserved, wall 32 may not beparallel to outer surface 26. Second and third portions 34, 36 withwalls 38, 40, respectively, define recesses into which end caps areplaced, as will be described shortly. Wall 38 of second portion 34 ispreferably perpendicular to top face 12, while shoulder 42 is preferablydisposed in a plane 44 parallel to plane 13. Similarly, wall 40 of thirdportion 36 is preferably perpendicular to bottom face 14, while shoulder46 is preferably disposed in a plane 48 parallel to plane 15. Alternateembodiments of central shaft 10 may not include shoulders 42, 46.Preferably, second and third portions 34, 36 are symmetrical about plane50, which is disposed halfway between points 18, 22 and runsperpendicular to central axis 24.

Second portion 34 of central shaft 10 will now be described, althoughthe foregoing description also applies to third portion 36. As can beseen in FIG. 1B, second portion 34 is symmetrical about line 52, andincludes opposing arcuate regions 54, 56 each having a radius ofcurvature R₁, and opposing arcuate regions 58, 60 each having a radiusof curvature R₂. Preferably, radius of curvature R₁ is between about 3.0mm and about 4.0 mm, and more preferably about 3.5 mm, while radius ofcurvature R₂ is between about 5.0 mm and about 6.0 mm, and morepreferably about 5.5 mm. Thus, second portion 34 is keyed such that alike-shaped portion of an end cap may be inserted therein in twoorientations, as also will be described shortly. Second portion 34 isgenerally square, with wall 38 having a maximum separation D₂ that ispreferably between about 12 mm and about 15 mm, and more preferablyabout 13.5 mm. Outer surface 26 of central shaft 10 preferably also hasan outer diameter D₃ between about 17 mm and about 20 mm, and morepreferably between about 18 mm and about 19 mm. Second and thirdportions 34, 36 each extend to a depth H₁ below top and bottom faces 12,14, respectively, of between about 3 mm and about 5 mm, and morepreferably about 4 mm.

Alternate embodiments of second and third portions 34, 36, respectively,may be round, square, diamond shaped, or star shaped, and preferably aresymmetrical about at least one central axis. Shapes with symmetry aboutmore than one central axis, such as a square that is symmetrical abouttwo diagonal axes that extending through opposing pairs of corners,provide additional versatility.

Referring now to FIGS. 2A to 2B, an end cap 70 suitable for coupling tocentral shaft 10 is shown. End cap 70 includes a base portion 72 with anouter wall 73 a and an inner wall 73 b, and a ridge portion 74. Baseportion 72 is sized to fit in a second or third portion 34, 36, withlower face 76 extending a distance of about H₁ so as to abut a shoulder42, 46. Base portion 72 is symmetrical about line 78, and includesopposing arcuate regions 80, 82 each having a radius of curvature ofabout R₁, and opposing arcuate regions 84, 86 each having a radius ofcurvature of about R₂. Thus, when base portion 72 is inserted into asecond or third portion 34, 36, each arcuate region 80, 82 will fit in acentral shaft arcuate region 54, 56, while each arcuate region 84, 86will fit in a central shaft arcuate region 58, 60. The remainingportions of outer wall 73 a are generally square, as described withrespect to second and third portions 34, 36. In an alternate embodiment,the remaining portions of outer wall 73 a may be another geometry suchas round. Thus, allowing for a slight variation in dimensions betweenbase portion 72 and second and third portions 34, 36, a press-fit may beachieved between an end cap 70 and central shaft 10.

Ridge portion 74 of end cap 70 includes a slot 88; an implant havingopposing end caps 70 with opposing slots 88 thus may be grasped by asurgeon using a suitable tool to facilitate placement of the implant inthe body. Thus, slot 88 may be used to guide insertion of an implantunder distraction. Preferably, slot 88 has a width W₁ of between about 7mm and about 9 mm, and more preferably about 8 mm. Ridge portion 74includes a first, upper face 90 with teeth 92, a second face 94, and athird face 96 formed by slot 88. Second and third faces 94, 96 aredisposed in planes 98, 100, respectively, which are preferably sloped atan angle E₂ with respect to each other. Preferably, angle θ₂ is aboutthe same as angle θ₁ as previously described with respect to centralshaft 10. In an alternate embodiment, the angulations of second andthird faces 94, 96 are different. In addition, teeth 92 preferablyextend to a plane 102 that is parallel to plane 100 and separated by adistance L₃. Preferably, distance L₃ is between about 1.7 mm and 2.1 mm,and more preferably about 1.9 mm. There is a minimum distance L₂ betweensecond and third faces 94, 96 and a maximum distance L₂+δ.

Hole 104 extends from upper face 90 to lower face 76. Preferably,dimensions D₁, D₄ are about the same and between about 10 mm and 12 mm,and more preferably about 11 mm. In alternate embodiments, dimensionsD₁, D₄ may be different from each other. As will be described withrespect to an end cap 210, shown for example in FIG. 6B, upper face 90of end cap 70 may be curvilinear such that teeth 92 are disposed along acurve rather than in a single plane as shown in FIG. 2A.

A variety of patterns and geometries of teeth 92 may be provided on endcap 70, and serve to resist migration of end cap 70 with respect toadjacent bony areas after implantation. In one embodiment, teeth 92 arepyrimidal in shape, with opposing pyrimidal edges disposed at an angle αwith respect to each other. Preferably, angle a is between about 50° andabout 70°, and more preferably about 60°. Alternatively, migrationrestricting structures such as saw teeth, regular teeth, spurs orgrooving may be provided.

Turning now to FIGS. 3A to 3C, constructions of skeletal reconstructioncages using a central shaft 10 and a pair of end caps 70 are shown. Asdiscussed earlier, top and bottom faces 12, 14, respectively, of centralshaft 10 have a minimum longitudinal height L₁ and a maximumlongitudinal height L₁+2δ, with the change in height from L₁ resultingfrom an increase in height of δ for each angle θ₁. Also, second andthird faces 94, 96 of end cap 70 are preferably sloped at an angle θ₂with respect to each other, with angle θ₂ being about the same as angleθ₁. Thus, the end caps 70 may be disposed in such a manner that thefollowing constructions of skeletal reconstruction cages 110, 120, 130are obtained: TABLE 1 Skeletal Reconstruction Maximum Minimum AngulationCage Height Height of End Caps 110 L₁ + 2L₂ + 3δ L₁ + 2L₂ + δ 3° 120L₁ + 2L₂ + 4δ L₁ + 2L₂ 6° 130 L₁ + 2L₂ + 2δ L₁ + 2L₂ + 2δ 0°

As listed in Table 1, the configurations of end caps 70 coupled to acentral shaft 10 permit cap angulations of about 0°, 3°, and 6°,respectively, assuming that each distance δ results from a separation θ₁or θ₂ of about 1.5°. For example, the angulation achieved by end caps 70on skeletal reconstruction cage 110 is determined by taking thedifference between the maximum height, L₁+2L₂+3δ, and the minimumheight, L₁+2L₂+δ, which difference is 2δ or about 3°. Referring to FIG.3D, a skeletal reconstruction cage 130 is shown disposed between a pairof vertebral bodies 145.

In addition, central shafts 10 may be provided with various maximumoverall heights L₁+2δ such as 14 mm, 24 mm, and 34 mm, and suitableminimum heights as required by the geometrical constraints describedabove. Similarly, end caps 70 may be provided with various overallmaximum heights L₄ such as 3 mm, 5 mm, 7 mm, 9 mm, and 11 mm, andsuitable minimum heights as required by the geometrical constraintsdescribed above. The present invention provides a means by which asignificant number of construct heights can be created using a smallnumber of different central shafts 10 and end caps 70. Thus, a kit ofskeletal reconstruction cages may be created for use by a surgeon, forexample, during corpectomy procedures. In particular, the kit mayinclude a variety of sizes of central shafts 10 and end caps 70 so thatfor a given height of void to be spanned by a skeletal reconstructioncage, the surgeon may construct a suitable cage. For example, a kit maybe created with central shaft 10 sizes of 14 mm, 24 mm, and 34 mm, aswell as end cap 70 sizes of 3 mm, 5 mm, and 7 mm. A kit with thesecomponents permits a surgeon to reconstruct skeletal reconstructioncages with overall maximum heights as listed in Table 2: TABLE 2 ShaftHeight First End Cap Second End Cap Overall Maximum (mm) Height (mm)Height (mm) Cage Height (mm) 14 3 3 20 14 3 5 22 14 3 7 24 14 5 5 24 145 7 26 14 7 7 28 24 3 3 30 24 3 5 32 24 3 7 34 24 5 5 34 24 5 7 36 24 77 38 34 3 3 40 34 3 5 42 34 3 7 44 34 5 5 44 34 5 7 46 34 7 7 48

As shown by Table 2, a kit with six sizes of components permits asignificant range in skeletal reconstruction cage heights (a 28 mm rangeis provided in Table 2). Notably, a kit only one shaft for each of thethree shaft heights and only two end caps for each of the three end capheights would require a total of about 126 mm of bone, while a kit withunitary cages (i.e., manufactured as one piece) for each of the 15heights in Table 2 would require about 612 mm of bone (assuming baseportions on caps of about 4 mm each in length). Thus, a substantialsavings is realized with a kit of the present invention. In addition,greater flexibility may be provided by providing a range of separationsθ₁ and/or θ₂ .

If height adjustment is desired at even smaller increments, washer-likestructures 150 may be provided for mounting, for example, on baseportions 72 of end caps 70, or alternatively within second or thirdportions 34, 36. As shown in FIG. 4A, structures 150 may be providedwith heights H₂, preferably between about 1 mm and about 4 mm, as wellas inner holes 152. Referring to FIG. 4B, skeletal reconstruction cage155 includes a first washer-like structure 156 mounted on a base portion72, and a second washer-like structure 158 disposed within a thirdportion 36. Preferably, structures 156, 158 have about the same heights.

Furthermore, although the embodiment of the present invention describedabove permits rotation of an end cap 70 by 180° with respect to acentral shaft 10, alternate mating configurations may instead be used topermit other rotations such as 90° (i.e., square mating configurations).Also, while the above-described end caps 70 and central shaft 10 eachinclude two pairs of opposing arcuate surfaces with different radii,other geometries may also be used to limit rotation of an end cap 70with respect to a central shaft 10. For example, rotation of 180° may beachieved using an elliptical or diamond shape. Such shapesadvantageously prevent undesired torsional rotation of an end cap 70with respect to a central shaft 10, and facilitate proper assembly of askeletal reconstruction cage by a surgeon.

End caps 70 may be offered with various configurations of slots suitablefor different surgical approaches, including lordotic, anterior,anterolateral, and lateral. Multiple slots such as parallel slots may beprovided, and the end caps may also have a variety of overall outerdiameters, inner diameters, and edges such as radiused edges, chamferededges, and flat edges. Depending on the size of cage that is required,the central shafts and end caps may be fabricated from a variety ofbones including the femur, humerus, tibia, fibula, radius, or ulna.

End caps 70 and central shafts 10 may be secured to each other using avariety of techniques. Preferably, a press-fit is used between thesecomponents. Alternatively, or in addition, one or more pins, screws, orother mechanical securing elements may be used such as pins 140 shown inFIG. 3C. As discussed above, other suitable manners for securing thecomponents include bonding agents or other chemical means. Alternatemechanical fasteners such as screws or keys, as described above, may beused. Other interfitting such as with interlocking features may be usedas well, including ribbing, threading, tapers, knurled surfaces,interference lips in which a lip on one component fits in a groove inanother component, flanges, or other joints. In addition, while skeletalreconstruction cages 110, 120, 130 are constructed with end caps 70 andcentral shafts 10 that have flat, mating surfaces, other types of jointsmay be employed to interfit these components including joints thatpermit articulation such as a ball and socket type of joint, andparticularly joints that permit firm interlocking between two componentsto prevent relative movement between the components. Preferably, mortiseand tenon joints can be used to interfit components of the skeletalreconstruction cages. Other coupling arrangements such as edge jointsincluding tongue and groove joints, rabbeted joints, toothed joints, anddovetail joints are also suitable for the present invention.

Holes 28, 104 in skeletal reconstruction cages 110,120, 130 may bepacked with a variety of materials. For example, a cancellous plug maybe inserted into holes 28, 104. Such a cancellous plug would serve topromote bone fusion, and could be highly concentrated or otherwisesoaked with bone growth substances or blood prior to insertion. Agreater degree of fluid absorption and/or concentration may be achievedusing a syringe or aspirator to draw blood or other fluids through theplug. Other packing materials include bone chips, slurries of boneparticulate, bone fibers, or bone-growth inducing substances.

Referring to FIGS. 5 to 6, an embodiment of a skeletal reconstructioncage suitable for use in the lumbar region of the spine is shown.Turning to FIGS. 5A to 5B, a central shaft 160 includes a top face 162and a bottom face 164, which preferably are nonparallel. Top face 162 isdisposed in a top plane 163 that is preferably sloped at an angle θ₃with respect to a horizontal plane 166 extending from the highestvertical point 168 of central shaft 160. Similarly, bottom face 164 isdisposed in a plane 165 that is preferably sloped in convergingorientation with respect to top face 162 at the same angle θ₃ withrespect to a horizontal plane 170 extending from the lowest verticalpoint 172 of central shaft 160. Preferably, angle θ₃ is between about 2°and about 3°, and more preferably about 2.5°. A wider range ofangulations may be used to meet the needs of voids in bones such as longbones.

Central shaft 160 is disposed about a central axis 174 and preferablyhas a central portion 175 with an outer surface 176 that is generallycylindrical. A hole 178 extends from top face 162 to bottom face 164,perpendicular to planes 166, 170. Hole 178 has a wall 180 that isgenerally parallel to outer surface 176 and defines an inner diameter D₅that is preferably between about 11 mm and 13 mm. As described above,the geometry of the natural bone canal and natural outer surface may beused, in which case wall 180 and outer surface 176 may not be parallelto each other. Central shaft 160 also includes upper and lower portions182, 184, respectively, with outer walls 186, 188, and which defineprotrusions onto which end caps are placed, as will be describedshortly. Wall 186 of upper portion 182 is preferably perpendicular totop face 162, while shoulder 190 is preferably disposed in a plane 192parallel to plane 163. Similarly, wall 188 of lower portion 184 ispreferably perpendicular to bottom face 164, while shoulder 194 ispreferably disposed in a plane 196 parallel to plane 165. Preferably,upper and lower portions 182, 184 are symmetrical about plane 198, whichis disposed halfway between points 168, 172 and runs perpendicular tocentral axis 174.

Upper portion 182 of central shaft 160 will now be described, althoughthe foregoing description also applies to lower portion 184. Referringin particular to FIG. 5B, upper portion 182 is symmetrical about line200. Preferably, upper portion 182 is generally elliptical, parabolic,or otherwise oblong with a major diameter D₆ along line 200 and a minordiameter D₇ along line 202. At the point at which wall 186 of upperportion 182 merges and becomes coplanar with wall 176 of central portion175, the radius of curvature R₃ is about the same as the radius ofcurvature of circular wall 176, and preferably is between about 8 mm and10 mm, and more preferably about 9 mm. Points on wall 186 of upperportion 182 at minor diameter D₇ on axis 202 have a radius of curvatureR₄ preferably between about 6.5 mm and about 8.5 mm, and more preferablyabout 7.5 mm. Thus, upper portion 182 is keyed such that a like-shapedportion of an end cap may be inserted thereon in two orientations, asalso will be described shortly. Circular wall 176 of central shaft 160preferably also has an outer diameter D₆ between about 17 mm and about20 mm, and more preferably between about 18 mm and about 19 mm. Upperand lower portions 182, 184 each have heights H₂ above and below planes192, 196, respectively, of between about 3 mm and about 5 mm, and morepreferably about 4 mm.

In one preferred embodiment, central portion 175 has a maximum length L₅of between about 13.5 mm and about 15.5 mm, and more preferably about14.5 mm. Other preferred lengths L₅ for central portion 175 arepreferably between about 23.5 mm and about 25.5 mm, and more preferablyabout 24.5 mm, as well as between about 33.5 mm and about 35.5 mm, andmore preferably about 34.5 mm. A set of three central portions may, forexample, be provided with maximum heights L₆ of about 22.5 mm, 32.5 mm,and 42.5 mm.

As shown in FIGS. 6A to 6E, an end cap 210 suitable for coupling tocentral shaft 160 includes an outer wall 212, as well as a central holedisposed along axis 213 with a lower inner wall 214, an upper inner wall216, and an inner ridge portion 218. Lower inner wall 214 extends abouta depth H₂ and is sized to fit snugly on an upper or lower portion 182,184 of central shaft 160 with an upper or lower face 162, 164 abutting ashoulder 218. Preferably, upper inner wall 216 has a dimension that isabout the same as dimension D₅ of hole 178 of central shaft 160. End cap210 is symmetrical about line 220, and is generally oblong in shape withfirst and second widths W₂, W₃. Notably, while outer wall 176 of centralshaft 160 is generally circular, outer wall 212 of end cap 210 isgenerally oblong, so that a generally I-shaped skeletal reconstructioncage may be formed when a pair of end caps 210 are placed on centralshaft 160. Preferably, first width W₂ is between about 26 mm and about34 mm, and more preferably about 30 mm, while second width W₃ is betweenabout 20 mm and about 28 mm, and more preferably about 24 mm. Also,preferably first and second widths W₂, W₃ are within about 4 mm andabout 8 mm of each other. In addition, preferably the sizing of centralshaft 160 and end caps 210 allows for a slight variation in dimensionsbetween lower inner wall 214 of end cap 210 and walls 186, 188 of upperand lower portions 182, 184, respectively, so that a press-fit may beachieved. Preferably, the wall thicknesses of end cap 210 are no smallerthan about 4 mm. Heights A and B of end cap 210, shown in FIG. 6C, maybe changed to provide different amounts of angulation.

End cap 210 includes a slot 222 for facilitating placement in the body.Preferably, slot 222 has a width W₄ of between about 8 mm and about 10mm, and more preferably about 9 mm. End cap 210 also has an upper face224 with teeth 226 to resist migration. Upper face 224 generally followsa curvilinear path and is convex, as shown for example in FIG. 6B. Thisgeometry is useful in mating with the natural anatomical shape of avertebral body, which is curved in the anterior-posterior plane.

Alignment indicia 228 such as a line along the side of end cap 210, asshown in FIG. 6E, may be provided on the outer surface of central shaftsand/or end caps. Preferably, indicia 228 is an imprint, i.e. with ink,although indicia 228 may instead be provided in the form of surfacescoring or a protrusion on the surface. Indicia 228 may serve to assistin properly orienting the components with respect to each other or withrespect to particular anatomical features during insertion into ananatomical void. Indicia 228 also may be used to indicate the angulationof end cap 210. The indicia suitable for the present invention includes,but is not limited to, markers such as lines, arrows, lettering, andsymbols.

As shown in FIG. 6F, a generally I-shaped skeletal reconstruction cage230 may thus be formed using a pair of end caps 210 disposed on centralshaft 160. An alternative arcuate body 235 may be used with a pair ofend caps 210 to form a cage 236, as shown in FIG. 6G. Body 235 isprovided with curvature so that body 235 provides angulation for endcaps 210.

Referring to FIGS. 7A-7E, another alternate embodiment of an end cap forcoupling to a central body such as central shaft 160 is shown. End cap240 includes an outer wall 242, as well as a central hole 243 disposedalong axis 244 with a lower inner wall 245, an upper inner wall 246, andan inner ridge portion 248. Lower inner wall 245 extends about a depthH₃ and is sized to fit snugly on an upper or lower portion 182, 184 ofcentral shaft 160 with an upper or lower face 162, 164 abutting ashoulder 248. Preferably, upper inner wall 246 has a diameter that isabout the same as diameter D₅ of hole 178 of central shaft 160. End cap240 is symmetrical about line 250, and is generally oblong in shape withfirst and second widths W₅, W₆. Notably, while outer wall 176 of centralshaft 160 is generally circular, outer wall 242 of end cap 240 isgenerally oblong, so that a generally I-shaped skeletal reconstructioncage may be formed when a pair of end caps 240 are placed on centralshaft 160. Preferably, first width W₅ is between about 26 mm and about34 mm, and more preferably about 30 mm, while second width W₆ is betweenabout 20 mm and about 28 mm, and more preferably about 24 mm. Inaddition, preferably the sizing of central shaft 160 and end caps 240allows for a slight variation in dimensions between lower inner wall 245of end cap 240 and walls 186, 188 of upper and lower portions 182, 184,respectively, of central shaft 160 so that a press-fit may be achieved.Thus, the dimensions of lower inner wall 245 are such that major andminor diameters D₆, D₇ of central shaft 160 are about the same as widthsW₇, W₈, respectively, of end cap 240. Central hole 243 may have aboutthe same diameter D₈ as diameter D₅ of hole 178 of central shaft 160,although the diameter may be smaller or larger to fit a particular need.In one embodiment, end cap 240 has a maximum height L₇ of between about12 mm and about 14 mm, and preferably about 13 mm.

End cap 240 also has an upper face 250 with teeth 252 to resistmigration. Upper face 250 is generally convex, as shown for example inFIG. 7B along line 254, and thus may positively engage surrounding,concave anatomical tissue with similar geometry. The side view of FIG.7B is taken along line 241, proximate the point 247 at which line 241and end cap 240 intersect. Another side view taken along line 250 isshown in FIG. 7D.

Although press-fitting of end caps 240 on central shaft 160 has beendescribed, other interfitting such as with interlocking features andjoints described above may be used.

Another embodiment of a skeletal reconstruction cage 260 is shown inFIG. 8A. A threaded central strut 262 is provided with end caps 264, 266that are threadably associated with central strut 262. End caps 264, 266have threaded bores 268, 270, respectively, which threadably receivecentral strut 262. Preferably, right-handed threading is provided oncentral strut 262 proximate one of ends 274, 276, while left-handedthreading is provided proximate the other end. The threading on end caps264, 266 corresponds to the type of threading at a given location oncentral strut 262. Thus, the overall length L₈ of skeletalreconstruction cage 260 may be changed by screwing action of centralstrut 262 without rotational movement of end caps 264, 266. To aid inturning central strut 262 with respect to end caps 264, 266, athrough-hole 273 is provided for insertion of a rod or other suitabledevice. A through-hole 272 extends from one free end 274 to the otherfree end 276, and may be packed with such materials as bone chips or acancellous insert, as previously described. Notches 278, 280 may beprovided on free ends 274, 276, respectively, to facilitate handling ofthe device by a surgeon. For added structural integrity, washer-likestructures similar to previously described washer-like structures 150may be provided for mounting about central strut 262 between end caps264, 266 to fill the gap therebetween and provide a skeletalreconstruction cage with a uniform outer surface.

In an alternate embodiment, shown in FIG. 8B, skeletal reconstructioncage 284 is provided with end caps 264, 266 without slots 278, 280. Inaddition, pins 275 are provided to secure end caps 264, 266 to centralstrut 262 after a desired separation L₈ has been set. Once suitabledistraction has been achieved, holes may be drilled in end caps 264, 266for the insertion of pins 275 to maintain the desired distractionheight. Alternatively, caps 264, 266 may be provided with pre-drilledholes through which subsequent drilling is conducted for pin insertion.In addition, set screws may be used to lock central strut 262 in place.In some embodiments, end caps 264, 266 may be provided with angled orconvex free ends 274, 276, respectively. Other features may be providedsuch as tapering, threading, and ribbing, as described previously withrespect to other embodiments.

Once suitable separation is achieved between end caps 264, 266 of cages260, 284, a support member 285, as shown in FIG. 8C, may be insertedbetween end caps 264, 266 to further support the end caps. Preferably,support 285 is generally C-shaped, with a central arcuate groove 286that may generally conform to the outer diameter of central strut 262.Outer surface 287 preferably is sized with about the same outer diameteras end caps 264, 266. The C-shape of support 285 facilitates coupling tocentral strut 262, and in particular, arcuate groove 286 preferablyspans a circular arc of more than 180° so that support 285 may be flexedduring installation but clamps to central strut 262 to resist removal.Faces 288, 289 abut faces 282, 283 of end caps 264, 266, respectively.In order to achieve a proper fit, a support 285 may be cut so that ithas the desired height. Also, support member 285 may be fixed to endcaps 264, 266 and/or central strut 262, such as with one or moresuitable fasteners.

As shown in FIG. 9, a skeletal reconstruction cage 290 formed accordingto the present invention includes pair of end caps 292, 294 with a body296 disposed therebetween. Faces 293, 295 of end caps 292, 294,respectively, are generally parallel to each other, forming a cage 290in the shape of a parallelogram in cross-section, and are preferablydisposed at an angle of between about 30° and about 60° with respect toa plane parallel to body free ends 297, 298. The free ends 297, 298 aredisposed in planes that are generally parallel to each other andgenerally perpendicular to cylindrical outer surface 299. Cage 290 spansthe vacancy between bone sections 298, 300, which may for example be avacancy in the femur.

The implants contemplated by the present invention may be made ofallograft, autograft, or xenograft bone material as well, orcombinations of autograft, allograft, and xenograft bone material. Inaddition, the implants may also be formed from cancellous bone, corticalbone, or combinations thereof and the choice of such materials may bebased on the materials properties obtainable from a given type of bone.As discussed earlier, cancellous bone is available in a range ofporosities based on the location in the body from which the bone isharvested. While extremely porous cancellous bone may be harvested fromvarious areas such as the iliac crest, less porous bone may be harvestedfrom areas such as a tibial condyle. Thus, the materialsproperties—particularly the porosity—of the implants may be selected tomeet the needs of a given application. In addition, the implants of thepresent invention may be formed either partially or completely usingnon-bone materials such as metals, alloys, ceramics, polymers,composites, and encapsulated fluids or gels.

Turning to FIGS. 10A to 10H, a variety of pre-formed cancellous insertsmay be used as an osteoconductive filler with cages such as thosedescribed herein. Preferably, the cancellous bone is harvested from anyof the long bone condyles. One or more inserts may be used with a cageto meet the proper height requirements, for example, to substantiallyfill the cage. Cage 300 is oblong in shape, while cage 310 is round.Each cage 300, 310 may include a recessed region or through-hole region302, 312, respectively. Preferably, regions 302, 312 are packed withosteoinductive materials. Additional configurations of cancellousinserts are shown in FIGS. 10C and 10D. Inserts 320, 330 includeprotruding portions 322, 332, respectively, which are sized to receive acap. For example, as shown in FIG. 10E, a skeletal reconstruction cage340 includes a sleeve 342 with a insert 330 disposed therein. A cap 344is press-fit to protrusion 332. Perforations 346 extend through the wallof sleeve 342, exposing portions of cancellous insert 330 to surroundinganatomy when inserted in a bony region. Inserts such as those of FIGS.10A to 10D may be interfitted to permit greater insert lengths to beformed. For example, as shown in FIG. 10F, a composite insert 350 isformed of two inserts 352, 354; insert 352 includes a female portion353, while insert 354 includes a male portion 355. Female and maleportions 353, 355 are sized to mate, and may be formed, for example, ina groove and tongue configuration or a central recess and centralprotrusion configuration. The joints, fastening components, and othersecuring means previously discussed also may be used. The inserts may befashioned with through-holes for receiving osteoinductive substances. Asshown in FIGS. 10G and 10H, inserts 360 and 370 include through-holes ofvarying sizes and orientations. Through holes 362 in insert 360 extendfrom free end 364 to free end 366, while through-holes 372 of insert 370extend generally transverse to free ends 374, 376. In addition, each ofends 364, 366 and 374, 376 may be angulated, for example to accommodatelordosis. Through-holes 362, 372 may be filled with osteoinductivematerials.

The pre-formed inserts of the present invention also are particularlysuitable for use in skeletal reconstruction cages such as those formedfrom titanium mesh indicated for reinforcement of bony regions inorthopedic procedures and typically available in pre-formed round andoval-shaped cylinders. Preferably, sets of cancellous inserts areavailable for use with skeletal reconstruction cages. In one embodiment,oblong inserts are available with minor and major diameters,respectively, of: about 14.6 mm and about 19.6 mm, about 19.6 mm andabout 25.6 mm, and about 23.6 mm and about 30.6 mm. Round inserts may beavailable with outer diameters of 7.6 mm, 9.6 mm, and 12.6 mm. Thecancellous inserts may be provided in combination with cortical bone,which may in some embodiments be integrally formed therewith. Inaddition, some embodiments of the cancellous inserts may bedemineralized or partially demineralized. Alternative materials for theinserts described herein include metals, alloys, ceramics, polymers,composites, and encapsulated fluids or gels. Cage 340 may be a metallicmesh which receives a suitably sized cancellous insert, such as theabove-mentioned sizes.

Additional embodiments contemplated by the present invention includeskeletal reconstruction cages formed of non-symmetrical bone sections,or non-symmetrical components such as different sized end caps.

The embodiments of skeletal reconstruction cages disclosed herein mayinclude components that are initially provided with a first moisturecontent, but then allowed to assume a new configuration with a secondmoisture content. For example, in the embodiment shown in FIG. 3A, endcap 70 initially may be supplied with a first outer diameter and a firstinner diameter. Subsequent freeze-drying of end cap 70 results inshrinkage such that end cap 70 assumes a configuration with a secondouter diameter that is smaller than the first outer diameter, whilehaving a second inner diameter that is smaller than the first innerdiameter. When end cap 70 is rehydrated or treated with a swellingagent, end cap 70 may reassume a configuration with the first outerdiameter and first inner diameter. By providing a bone section such asan end cap 70 in the freeze-dried state while at least partiallydisposed inside another bone section such as a central shaft 10 that maybe loosely interference fit, rehydration of end cap 70 in place permitsa tighter interference fit to be achieved. Notably, a bone section withno inner diameter may shrink in outer diameter only when freeze-dried.Thus, similarly, an insert to be disposed centrally in the hole incentral shaft 10 may be the bone section that is rehydrated to provide atighter mating and interference fit with central shaft 10. Use of theseproperties can permit greater variation in dimensional tolerance betweenbone sections during manufacture, while tight final assembly can stillbe achieved. In addition, protrusions on bone sections become smallerwhen dehydrated, but expand when rehydrated; in contrast, recesses inbone sections become smaller when hydrated, but larger when dehydrated.Temperature changes may also be used to achieve better interferencefits.

The use of insertable securing elements such as keys, pegs, pins,wedges, or other suitable components in joints to assist in securingbone components such as end caps 70 and central shafts 10 to each otheris also an effective approach to providing a stable joint. Keys, forexample, may be inserted in notched or grooved areas in skeletalreconstruction cage components, serving as the securing element betweentwo or more components. Parameters that may be varied when usinginsertable securing elements, such as keys, include the angle ofapplication, the spacing of the elements, and the thicknesses of theelements.

While various descriptions of the present invention are described above,it should be understood that the various features can be used singly orin any combination thereof. The various types of joints and connectionscan be used on skeletal reconstruction cages of different sizes orconfigurations, such that the invention is not to be limited to only thespecifically preferred embodiments depicted in the drawings.

Further, it should be understood that variations and modificationswithin the spirit and scope of the invention may occur to those skilledin the art to which the invention pertains. For example, multiple,differently shaped and sized skeletal reconstruction cages can beconstructed to serve the desired purpose. Accordingly, all expedientmodifications readily attainable by one versed in the art from thedisclosure set forth herein are within the scope and spirit of thepresent invention and are to be included as further embodiments. Thescope of the present invention is accordingly defined as set forth inthe appended claims.

1. A skeletal reconstruction cage comprising: a central body having afirst end, a second end, and a hole extending therebetween; a first endcap; a second end cap; and a pre-formed cancellous bone insertconfigured to be inserted into the hole; wherein the first end cap isdisposed proximate to the first end of the central body, and the secondend cap is disposed proximate to the second end of the central body; andwherein at least one of the end caps is formed of cortical bone.
 2. Thecage of claim 1, wherein the insert has a first end and a second end,and wherein the first end cap is coupled to the first end of the insert,and the second end cap is coupled to the second end of the insert. 3.The cage of claim 2, wherein the first end cap is press-fit onto thefirst end of the insert.
 4. The cage of claim 1, wherein at least one ofthe insert and end caps is at least partially demineralized.
 5. The cageof claim 1, wherein the insert substantially fills the hole.
 6. The cageof claim 1, wherein the central body has a plurality of perforations soas to expose a portion of the insert.
 7. The cage of claim 1, whereinthe central body is substantially mesh-like.
 8. The cage of claim 7,wherein the central body is comprised of titanium.
 9. The cage of claim1, wherein the insert has a diameter between about 7 mm and about 31 mm.10. A skeletal reconstruction cage comprising: a central body having afirst end, a second end, and a hole extending therebetween; a first endcap; a second end cap; and a pre-formed cancellous bone insertconfigured to be inserted into the hole; wherein the hole has a firstcross-sectional shape, and the insert has a second cross-sectionalshape; and wherein the first cross-sectional shape is substantiallydifferent than the second cross-sectional shape.
 11. The cage of claim10, wherein the first cross-sectional shape is substantially oval. 12.The cage of claim 10, wherein the second cross-sectional shape issubstantially circular.
 13. A skeletal reconstruction cage comprising: acentral body having a first end, a second end, and a hole extendingtherebetween; a first end cap; a second end cap; and a pre-formedcancellous bone insert configured to be inserted into the hole; whereinthe insert comprises at least a first through-hole extendingtherethrough.
 14. The cage of claim 13, wherein the insert has a firstend face and a second end face, and wherein the first through-holeextends from the first end face through to the second end face.
 15. Thecage of claim 13, wherein the insert has a first end face and a secondend face, and wherein the first through-hole extends substantiallytransverse the first and second end faces.
 16. The cage of claim 13,wherein the insert has a first end face and a second end face, andwherein the first through-hole is substantially angulated with respectto the first and second end faces.
 17. The cage of claim 13, wherein thefirst through-hole is configured to receive an osteoinductive material.18. A skeletal reconstruction cage comprising: a central body having afirst end, a second end, and a hole extending therebetween; a first endcap; a second end cap; and a pre-formed cancellous bone insertconfigured to be inserted into the hole; wherein the insert is formedfrom at least a first insert and a second insert.
 19. The cage of claim18, wherein the first insert is secured to the second insert.
 20. Thecage of claim 18, wherein the first and second inserts are mated in agroove and tongue arrangement.
 21. A skeletal reconstruction cagecomprising: a central body having a first end, a second end, a length,and a hole extending therebetween; a first end cap; a second end cap;and a pre-formed cancellous bone insert having a length, and configuredto be inserted into the hole; wherein the length of the insert isgreater than the length of the length of the central body.
 22. The cageof claim 21, wherein the insert has a first end and a second end, andwherein when the insert is inserted into the hole, the first end of theinsert extends beyond the first end of the central body, and the secondend of the insert extends beyond the second end of the central body.